(a) Field of the Invention
This inventive concept relates to semiconductor technology, or more specifically, a photomask manufacturing method.
(b) Description of the Related Art
As the critical dimension of semiconductor devices decreases, it is becoming increasingly difficult to use lithography technique to manufacture a photomask of small critical dimension. To further increase the integration level of semiconductor devices, double patterning techniques, such as Self-Aligned Double Patterning (SADP), have been proposed for photomask manufacture.
FIGS. 1A, 1B, and 1C show schematic sectional views illustrating a conventional photomask manufacturing method.
Referring to FIG. 1A, in a conventional manufacturing method, an etch material layer 102 is first formed on a substrate 101, then a sacrificial layer 103 is formed on the etch material layer 102, and a photomask layer 104 is formed on an upper surface of the etch material layer 102 and on an upper surface and an side surface of the sacrificial layer 103.
Referring to FIG. 1B, the photomask layer 104 on the etch material layer 102 and the sacrificial layer 103 is etched away, while the photomask layer 104 on the side surface of the sacrificial layer 103 is retained.
Referring to FIG. 1C, the sacrificial layer 103 is removed and the remaining photomask layer 104 is retained and becomes the photomask 114.
The photomask 114 manufactured by this conventional method has an asymmetrical shape. As shown in FIG. 1C, it has a straight side on one side but a curved side on the other. If this photomask is used to etch the etch material layer 102, different amount of the etch material layer 102 will be etched on two sides of the photomask 114, which will result in an asymmetrical surface on two sides of the photomask 114. Hence a photomask manufacturing method that can remedy this shortcoming is desirable.